Closed Loop Gravimetric Technology improves Productivity, Profitability and Quality

Raw material accounts for up to 70% of many plastics processing companies’ total operating costs. Clearly, if processors cannot control these costs they are seriously compromising their ability to control profit.

There are 3 basic methods to control raw material in production: centrally dosing and mixing by hand; installing devices that volumetrically dose and mix materials and gravimetric devices that dose and mix by weight.

Polymation is frequently asked, “How do I calibrate a volumetric feeder?”

The basic reasons why so many processors are making this request relates to the fact that inconsistent bulk density of materials is common place and when virgin, regrind and expensive colour and additives materials are blended together the effect is to compound inaccuracy, increase scrap and compromise product quality and consistency.

Dosing materials by volume via a cup method, or automated by an Auger Screw or Rotating Disk, fundamentally ensures there is a fixed volume for material to fill. Due to varying bulk density in size and shape of pellets this means in one volumetric dispense there could be 15 pellets but in the next 25 = built in error.

Furthermore, those companies that recognize these problems and prefer to hand weigh and mix materials introduce the potential for human error and even in countries where labour rates are considered low cost, the problems of centrally weighing and mixing materials leads not only to a high utilization of labour but also, an increased risk of redundant blends, congested production areas and a strong propensity for product inconsistency as conveying blends from large day bins leads to de-mixing over the production cycle.

Improving Product Quality and Saving Cost

Automatic calibration of each material ensures that optimum product quality is always achieved. Blow moulders and Injection moulders using gravimetric blending, automatic material handling, inline granulators and conveyor belts gain significant advantage over their non-automated competitors. A Closed Loop production principle that automatically grinds the product sprues or top and tails in the case of blow molding, and loads them into a gravimetric blender is the optimum solution for controlling production costs.

Material blends are then weighed directly in accordance with the production settings ensuring that weight rather than volume dictates the quality of the end product. Savings occur at every level of production. Colour and additives can be effectively added just to the virgin material saving as much in percentage terms as the regrind content of these expensive additives. Hidden savings of redundant blends, the mass transit of regrind and blended materials to and fro in production is also avoided, the unknown human error and the lack of production data that gravimetric control provides the producer is lost via manual or volumetric means.

Return on Investment is critical and PolyMation knows from experience that automated gravimetric Closed Loop production pays back in most cases in less than 12 months.

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